Central heating water query

[robgraham]

Daughter's house - I'm not sure that the radiator in the spare bedroom has ever been fitted since the a***e of a partner she was living with then inst alled the CH system. One bit of good judgement is that the house is in her name and she threw him out several years ago, but Dad has had to pick up th e pieces and sort out some horrors since then.

Anyway I fitted this radiator this morning, turned on the valves and of cou rse discovered leaks. Turned off valves and drained to get horribly black water.

I think that this indicates a system that has been running without any inhi bitor.

1 Am I right ?

2 If so what now ?

3 It's a combi boiler system - how does that influence whatever I have to do ?

4 Does a combi CH system some specific procedure for making up lost water / adding a radiator; that is, does it have some way of overcoming the lack of a header tank?

Thanks for any help. Rob

[Roger Mills]

Probably

Drain and flush it and refill with clean water plus inhibitor

Doesn't really matter. The CH circuit is a sealed circuit which is separate from the HW system. The boiler uses a diverter valve to determine which circuit to heat at any given time.

It will have a filling loop and pressure vessel. [Someone will be along with the URL of the Wiki on sealed systems].

[John Rumm]

[John Rumm]

Quite possibly

If you want to do a proper job, add a system cleaner and let that circulate for a while (up to two weeks max), then drain down, flush and refil.

Not really. Its probably also a sealed system, which means no header tank, and it will already have a filling loop which makes mains pressure flushing easy. (i.e. open a drain point, turn on the filling loop, then manipulate the rad valves so as to direct all the flow through each rad in turn (making sure to never close off all paths through the system))

Procedure in detail here:

Yes, there will be a filling loop - normally a pair of valves that comprise a tap and a non return valve that allow water to be injected from the cold main into the system (but not return via the same route). The final connection usually completed via a detachable braided hose. Some boilers have them built in, most don't. See the sealed system FAQ for details.

[RJH]

I had a combi sealed system boiler fitted, replacing an old open system. The system was power flushed at least twice by the plumber, but water still ran murky. Now, after I've refilled it a couple of times the water runs clear, but there's still black sediment in the rads.

The sediment has the consistency of old engine oil. My guess is that it's a combination of, in the main, 'spent' inhibitor and dirt that found its way in through the header tank.

I reckon the only way to get rid of it is to remove the radiators, turn them upside down, and flush. Took about 2 hours with a hose connected before it ran clear on one of the downstairs radiators. Upstairs don't seem as bad.

I don't know if it does any harm. I only bother if I'm removing the rad for some other reason.

[newshound]

What they said.

And if, in the future, you start finding the DHW supply running too cool, it will probably be a blockage in the primary side of the heat exchanger (from the black stuff). Best to remove this for cleaning, if you need to (some are rather inaccessible).

[newshound]

The sediment is mainly a black rather than brown form of iron oxide known as magnetite (because it is magnetic). Hence you can trap circulating oxide with a magnetic "filter". The stuff which has settled in the bottom of rads does no harm unless it gets disturbed, in which case there is a risk of blocking boiler heat exchangers, etc.

Agreed

That's what I do.

[Adam Funk]

I notice you wrote "*probably* also a sealed system" --- are there such beasts as cistern-fed combi-boiler systems?

[John Rumm]

There are (or at least were) some... WB used to do one, and Intergas possbily still do. I have also seen suggestion that Vaillant had a way of conventing theirs to open vent. Got a feeling Tim W fitted a vented one not long ago, or was that a system boiler (which is near enough a combi anyway)